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Chapter 7 Liquid‐liquid extraction of iridium(III) from malonate media using liquid anion exchanger
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur
227
CHAPTER-7
LIQUID-LIQUID EXTRACTION OF IRIDIUM(III) FROM MALONATE MEDIA USING LIQUID ANION EXCHANGER
7.1 Introduction
The recovery of platinum group metals (PGMs) such as Ir, Ru and Rh
from different matrices is always a challenging task for a chemist. The great
aesthetic value and technological importance of these metals has created a
never-ending demand [1]. These metals are scarce and have a wide range of
industrial applications. The determination of iridium has always been difficult.
The extremely inert character of iridium complexes creates a most challenging
problem in their separation. Recovery of iridium from spent catalysts and
recycling is economically important [2, 3]. In the recycling industry, there are
three main categories of refining materials. Primary materials such as gold-
/silver ore and PGM concentrates come directly from the mining industry. The
most important category, secondary materials, includes chemical/petrochemical
catalysts, automotive catalysts, and sweeps or bullion-type material from
numerous industrial applications. A third category of growing importance is
called “tertiary material” and consists of waste from other precious-metal
refining plants, such as insolubles from wet chemical operations, PGM sweeps
from Ag/Au refiners, and Ir-/Ru-/ Rh-concentrates [4].
Several extraction methods have been developed for iridium [5-8].
These falls into general types: ion-pair formation or formation of a neutral
coordinated complex. The first mechanism is greatly influenced by the charge
and the degree of aquation of the complex anion in the aqueous phase. The
second mechanism requires a ligand substitution reaction which, for these
metals, is very slow; heating the solution containing extractant or use of tin(II)
chloride (or bromide) as a labilizing agent is therefore usually necessary.
Although working at high temperatures or in the presence of tin salts is
acceptable in analytical procedures, the usefulness of such measures in large-
scale separations is dubious.
Chapter 7 Liquid‐liquid extraction of iridium(III) from malonate media using liquid anion exchanger
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur
228
7.2 Review of literature for liquid-liquid extractive separation of
Iridium(III)
High molecular weight amines (HMWAs) were first used as extractants
by Smith and Page [9]. The extraction of Iridium(III) from hydrochloric acid
and hydrobromic acid with 5 % tri-iso-octylamine solution in carbon
tetrachloride has been studied [10]. A liquid-liquid extraction of iridium(IV)
from chloride solution was studied under different condition of aqueous and
organic phase concentration using alamine-336 [11-15] as an extractant. The
extraction of iridium from its chloride solution was carried out using
commercially available solvent extraction reagents alamine 300 [15] and
aliquat 336 [15, 16]. Liquid-liquid extraction of iridium(III) and separation of
it from other platinum group metals (PGM) from Cl2/HCl leaching of the ores
or concentrations converted into thiourea eluate resin were studied, with high
molecular weight tertiary amines as extractants [17]. The use of
N-n-octyaniline [18] for the extraction of iridium(III) from malonate media was
studied at pH 8.5. Iridium(III) extracted in the organic phase was stripped with
2 M hydrochloric acid and was determined spectrophotometrically by stannous
chloride-hydrobromic acid method at 385 nm. Carbonyl-chloride complexes of
iridium extracted with tri-octylamine (TOA) [19] in isoamyl alcohol. The
extraction of iridium with 4-(non-5-yl)pyridine (NP) [20] was investigated.
Spectroscopic studies indicate that the extracted species is an ion pair. 4-
Octylamino pyridine [21] was used for determination of iridium(III) by
extraction and atomic emission spectrometry with inductively coupled plasma
source. Ideal conditions for extraction of iridium(III) with
2-mercaptobenzothiazole [22-25] into organic solvent have been established.
The stoichiometry of metal to reagent has been evaluated and an Ir192
radiotracer study of [25] of iridium extraction from greater than 1 M HCl acid
has been determined. The substituted thioureas such as N,N'-Dipyridylthiourea
[26] and N,N-diethyl-N'-benzoylthiourea (DEBT) [27] have been used for
solvent extraction of iridium(III). Also N-benzoyl-NN’-dihexyl thiourea [28]
and N-mono-and N,N-di-substituted benzoylthiourea [29] are used for
Chapter 7 Liquid‐liquid extraction of iridium(III) from malonate media using liquid anion exchanger
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur
229
extraction of iridium(III). A method was developed for solvent extraction
separation of trace amounts of iridium(III) from noble metal mixture by
thiobenzanilide [30,31]. N-o-tolyl-α-thiopicolinamide [31] and N-phenyl-5-
ethyl-α-thiopicolinamide [31] were used for separation of iridium from other
noble metals by extraction. Extraction of iridium was with 1,3-mono-
thiodicarbonyl [1-carbonyl-3-thioxo] compounds [32] in the presence of
labilizing agents at 85oC temperature from slight acidic media in to chloroform.
However, in a single extraction with chloroform, upto 92 % extraction of
iridium(III) was found from technical chloride solutions. The chloroform
extraction of iridium from 0.1-8 M sulphuric acid in the presence of potassium
ethyl xanthate [33] has been studied. Depending on the acid concentration,
iridium was partly extracted. Complexation and solvent extraction of iridium
with di-propyle sulfide [34] was studied by means of IR, UV, and PMR
spectroscopy. The solvent extraction of iridium(IV) from hydrochloric acid
solution by some dialkyl sulfoxides [35] of the types R2SO, RR'SO and R'2SO,
where R = alkyl and R' = cycloalkyl, was investigated. Solvent extraction of
iridium(III) and iridium(IV) chloride complexes from hydrochloric acid and
chloride solution by a sorbent MITKhAT [36] containing sulfur and nitrogen
was studied. The most probable mechanism of sorption and the complexation
of an iridium complex formed were proposed.
The extraction of iridium(III) from its chloride solution was carried out
using different commercially available solvent extraction reagents such as
cyanex 921 [15], cyanex 923 [15, 37-39], cyanex 471 [13, 37], cyanex 272,
LIX 54 [15], LiX-860N-I [15] and tri-butyl phosphate [15, 40-41]. The
distribution coefficients for the iridium were determined under different
concentrations of Cl-and H+ ions in the aqueous phase [15]. The splitting of a
system from biphasic to triphasic was studied in the liquid-liquid extraction of
Ir(IV) and HCl using cyanex 923 (C923) [38]. Solvent extraction of
iridium(III) with bis-(2-ethyl-hexyl) hydrogen phosphate (HDEHP) from
thiourea chloride [42] chloride media [43] was investigated. Iridium(III)
extracted was only 11.5 %. Separation and refining of iridium(III) by
Chapter 7 Liquid‐liquid extraction of iridium(III) from malonate media using liquid anion exchanger
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur
230
continuous solvent extraction with trioctyl phosphine oxide [44] has been
studied with high sensitivity. Extraction of iridium with triphenylphosphine
(TPP) [45] in 1,2-dichloroethane from hydrochloric acid medium has been
examined. Addition of stannous chloride as labilizing agent makes possible a
group separation of platinum metals. Identification is made with benzidine,
which is oxidized by iridium(IV) to a blue compound. Iridium(III) was very
efficiently removed from solutions containing rhodium(III) and a number of
metals ions by extracting the Triphenyl propylphosphonium salt [46] of the
iridium(III) chlorocomplex into chloroform. Interference of Pd(II), Pt(IV) and
Os(IV) is prevented by preliminary extraction of same reagent.
A new method for the separation and spectrophotometric analysis of
iridium by biphasic extraction system of n-propyl alcohol-sodium chloride –
water [47] was studied. The method was used for the determination of iridium
from Pt-Pd-Ir alloy samples. pH effect was studied on solvent extraction of
iridium(III) sulfates with N-octyl, N,N-dioctyl aniline and N,N,N-trioctyl
anilinium O,O-di(iso-propyl)dithiophosphates [48]. Solvent extraction behavior
of iridium(III) with salicylhydroxamic acid (SHA) [49] in isobutanol from
aqueous chloride solution was studied and compared with similar extraction
behavior of rhodium(III) and ruthenium(III). The formation of ion-pairs of
iridium(III) with pyruvic acid acylhydrazones and cyanine dyes, derivative of
1,3,3-trimethyl-3H-indolium [50] was studied. Iridium(III) could be determined
by this technique in synthetic mixtures in the presence of rhodium. Solvent
extraction of iridium by α-n-nonylpyridine-N-oxide (NPO) [51] from chloride,
sulfate, perchlorate, and nitrate solution was examined. NPO effectively
separates Pt and Ir by extraction from 0.5-1.0 M HCl. N-Hexyl iso-octylamide
[52] was used as an extractant for separation of iridium(IV) from rhodium(III).
Water was the most efficient stripping agent for reverse extraction of
iridium(IV). Iridium(III) was separated from a large excess of platinum by its
extraction with isoamyl alcohol-isobutyl methyl ketone [53] mixture graphite
furnace atomic absorption spectrometry using the method of standard addition
was then used to determine the metals with satisfactory precision and accuracy.
Chapter 7 Liquid‐liquid extraction of iridium(III) from malonate media using liquid anion exchanger
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur
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In present investigations, extraction behavior of iridium(III) using
n-octylaniline, a high molecular weight amine in toluene as an extractant was
carried out in presence of malonate media. The extraction system was
developed by checking various physicochemical parameters such as effect of
pH, extractant concentration, diluents, equilibrium period. The conventional
slope analysis method was employed for analysis of species formed in organic
phase. Also effect of various foreign ions on the extraction of iridium(III) was
studied and tolerable amount of each ion was detected. The studies also
extended to separate the iridium(III) from associated elements.
The various investigated systems are presented in tabular form in table
7.1 to review the literature in terms of various extractants used and special
characteristics regarding those systems.
Chapter 7 Liquid‐liquid extraction of iridium(III) from malonate media using liquid anion exchanger
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur
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Table 7.1 Summary of methods of solvent extraction of iridium(III)
System Aqueous phase
Organic phase Special features Ref.
No. Tri-iso-octyl amine (TIOA)
HCl< 4 M Carbon tetra-chloride
Rapid procedure. 10
Alamine 336 (A336)
HCl Kerosene Method was applicable for Ru(III) and Rh(III) also.
11
pH 2-3 - Method was applicable for other PGMs
12
HCl The percentage of Ir(III) increases with increasing HCl concentration of up to 8 M. Extraction was much higher
than TBP.
13, 14
Ir(III) separated from Rh(III).
14
Alamine 300 HCl _ Method was applicable for Ru(III) and Rh(III)
15
Aliquat 336 HCl - Method was applicable for Ru(III) and Rh(III)
15, 16
Stripping by aqueous ammonia.
Tertiary amines Cl2 / HCl - Iridium(III) separate from other platinum group metals (PGM) from Cl2/HCl leaching of the ores or concentrations converted into thiourea eluate resin were studied
16
N-n-octyaniline Sodium malonate
Xylene Method was applicable for the separation of iridium(III) from rhodium(III).
Iridium(III) was backstripped by 2 M HCl.
18
Tri-octylamine (TOA)
- Isoamyl alcohol
Carbonyl-chloride complexes of iridium extracted
19
4-(non-5-yl) pyridine
- Chloroform Method was applicable for Rh(III)
20
4-octylamino- pyridine
HCl, 1 M Chloroform The PGMs showed no mutual interference.
21
Chapter 7 Liquid‐liquid extraction of iridium(III) from malonate media using liquid anion exchanger
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur
233
2-mercapto benzothiazole
- HCl, 7.1 M
Chloroform -
Analysis of real samples. 1.5 h heating Oxygen containing inert
solvent improved extraction. In benzene, carbon tetra-
chloride or hexane forms voluminous white precipitate at interface of aq./org. phase.
22-25
N,N'-Dipyridylthiou-rea
- Chloroform Method was applicable for Os(VI)
26
N,N-diethyl-N'-benzoylthiourea (DEBT)
HCl, 2.0 M
Toluene Selectivity in the order Pd(II)>Pt(II)>Ru(III)>Rh(III)>Ir(III) when ligand/metal ratio becomes >4.
27
N-benzoyl-NN’-dihexyl thiourea
pH, 3 Solvesso 150 Cu, Fe co-extract Heating at 950C
28
N-mono and N,N-di-substituierten benzoylthiourea
HCl, 2 M Toluene Separation of Ir from other platinum group metals. Extraction more efficient at
80oC
29
Thiobenzanilide Thiourea, 0.2 M HCl, 0.5 M
Chloroform butanol (7:1) Chloroform
Method used for the deter-mination of Ir in materials rich in Fe and non-ferrous metals. Rapid method for determi-
nation of noble metals at ppm level. KI and SnCl2 labilizing
agents
30, 31
1,3-Mono-thiodicarbonyl [1-carbonyl-3-thioxo] compounds
Acetate buffer pH = 5-7
- Heat at 80oC for 1 h. 92 % recovery of Ir
32
Potassium ethyl xanthate
- Chloroform
Method used for extraction of 30 elements
33
Dipropyl sulfide
- - Method also used for extraction of Pt, Rh and Ru
34
Dialkyl sulphoxide
HCl - Method was applicable for other PGMs
35
MITKhAT HCl - Extraction of iridium(III) and iridium(IV)
36
Chapter 7 Liquid‐liquid extraction of iridium(III) from malonate media using liquid anion exchanger
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur
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Cyanex- 923 (C923)
HBr Toluene Iridium(III) separated from Pt(IV), Pd(II), and Rh(III)
Extraction of Ir(III) decreased with the increased concentration of stannous chloride.
Exothermic reactions
37
HCl and NaCl
n-octane, n-nonane, n-dodecane, kerosene, cyclohexane, toluene, and xylene
Third phase formation in the solvent extraction system Ir(IV)
38
HCl Toluene Recovery from spent autocatalysts
39
Cyanex 272, LIX 54, Cyanex 471, Cyanex 921, LiX-860N-I
HCl, HBr
Toluene Also applicable for other PGMs.
15, 37
Tri-butyl phosphate
HCl, 3.5-6 M
Toluene Monomeric anionic chloro complexes and polymeric aquachloro or aqua-oxo-complexes produced.
Rhodium(III) and Iridium(IV) separated from each other.
15, 40-41
Bis-(2-ethyl-hexyl) hydrogen phosphate (HDEHP)
HCl, 0.2 M pH=4.05 HCl, 0.5 M and thiourea 0.5 M pH,4.50
Isopar M 11.5 % Ir(III) extracted
28.5 % Ir(III) extracted. 95 % Back extraction into
1 M HCl
42, 43
Trioctyl phosphine oxide
- - Ir(III) purity of 99.99 % Separation of other PGMs
also studied. continuous solvent extraction
44
Triphenyl-phosphine
HCl 1,2-Dichlo- roethane
Stannous chloride used as labilizing agent. Useful for group concen-
tration before determination by AAS.
45
Chapter 7 Liquid‐liquid extraction of iridium(III) from malonate media using liquid anion exchanger
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur
235
Triphenyl propylphos- phonium chloride
Ascorbic acid 0.5 %; HCl, 4 M
Chloroform Method applied for identification of Ir in alloys and ores.
46
n- propyl alcohol-sodium chloride
HCl - Separation of iridium from Pt(IV), Pd(II), Rh(III) and Au(III) Determination of iridium in
Pt-Pd-Ir alloy samples.
47
N,N,N-trioctyl aniliniumO,O-di(iso-propyl)dithio-phosphates
- - Method was applicable for platinum and rhodium.
48
Salicylhydro-xamic acid(SHA)
HCl Isobutanol Separation of iridium from rhodium and ruthenium
49
1,3,3-trimethyl-3H-indolium
pyruvic acid
- Method was applicable for rhodium.
50
α-n-nonylpyridine-N-oxide (NPO)
0.5-1 M HCl
- Effectively separates Pt(IV) and Ir(III) by extraction
51
N-hexyl isooctylamide
HCl - Effectively separates Ir(III) and Rh(III) by extraction
52
MIBK HCl
- Pre-equilibration with water to remove platinum. The method of standard
addition should be used
53
Chapter 7 Liquid‐liquid extraction of iridium(III) from malonate media using liquid anion exchanger
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur
236
7.3 Experimental
7.3.1 Instruments
An Elico digital spectrophotometer Model 12 Chemito 215D with 1 cm
quartz cells was used for absorbance measurements and pH adjustments were
carried out using an Elico digital pH-meter Model LI-127. All weighing
operations were carried out by using Tapson’s analytical single pan balance
model 200 T having 0.001 g accuracy.
7.3.2 Chemicals and solutions
A stock solution of iridium(III) was prepared by dissolving 1 g of
iridium trichloride hydrate (Johnson Matthey, UK) in dilute analar
hydrochloric acid (1 M) and diluting to 250 mL with water and standardized
gravimetrocally [54]. A working solution of 50 µg/mL was made from it by
diluting the stock solution with water.
n-Octylaniline
The extractant n-octylaniline was prepared by the method of Pohlandt’s
[55] and its 0.2 M solution was prepared in xylene. All other solutions were
prepared from A. R. grade reagents and aqueous solutions were prepared using
water. Double distilled water used throughout the experimental study.
Standard solution of diverse ions were prepared by dissolving AR grade
reagents in water or dil HCl. All the organic solvents were used after double
distillation. All chemicals used were of AR grade.
7.3.3 General extraction and determination procedure for iridium(III)
An aliquot of 50 μg iridium(III) solution was mixed with a sufficient
quantity of sodium malonate to make its concentration 0.06 M in a total
volume of 25 mL of the solution. The pH of the aqueous solution was adjusted
to 8.0 by dilute sodium hydroxide and hydrochloric acid solution. The solution
was then transferred to a 125 mL separating funnel and shaken with 10 mL of
0.2 M n-octylaniline in toluene for 3 min. After separating the two phases, the
aqueous phase was discarded and the organic phase was stripped with two
Chapter 7 Liquid‐liquid extraction of iridium(III) from malonate media using liquid anion exchanger
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur
237
10 mL portions of 2 M hydrochloric acid solution. The stripped aqueous phase
was evaporated to moist dryness and extracted into water. The residue was
dissolved in minimum amount of 1 M hydrochloric acid and transferred into
25 mL volumetric flask and then 5 mL of concentrated hydrobromic acid was
added to it. The solution was mixed well and heated for 10 min in boiling water
bath, then to the same, 5 mL 25 % stannous chloride in concentrated
hydrobromic acid was added, mixed well and again heated for 2 min. The
cooled solution was diluted to 25 mL with water, and the absorbance was
measured at 400 nm against a blank solution. The concentration of iridium(III)
was computed from the calibration curve in similar manner [56].
7.4 Results and discussion
7.4.1 Extraction as a function of pH
The extraction studies of iridium(III) was performed at fixed
concentration of 0.06 M sodium malonate and between pH 1-10 with a 0.2 M
solution of n-octylaniline in toluene (Table 7.2). The pH range observed for the
quantitative extraction was 7.0-8.5 with n-octylaniline. Hence, the extraction of
iridium(III) were carried out at pH 8.0 for all extraction experiments (Fig. 7.1).
7.4.2 Effect of n-octylaniline concentration
Extraction of iridium(III) was carried out with various concentrations of
n-octylaniline in toluene. To optimize the extraction condition, other
parameters like pH, period of equilibration and diluent were kept constant. The
extraction was found to be increased with increasing reagent concentration.
The extraction of iridium(III) was quantitative in the range 0.12 M to 0.30 M
of n-octylaniline in toluene (Table 7.3). However, 10 mL of 0.2 M
n-octylaniline in toluene was recommended for general extraction procedure
(Fig. 7.2).
7.4.3 Effect of weak organic acid concentration
The extraction of iridium(III) was examined at pH 8.0 with 0.2 M
n-octylaniline in toluene in presence of varying concentrations from
Chapter 7 Liquid‐liquid extraction of iridium(III) from malonate media using liquid anion exchanger
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur
238
0.005 - 0.1 M of various weak organic acids (Table 7.4). The extraction of
ion-pair complex of iridium(III) was found to be quantitative in the range of
0.050 – 0.065 M sodium malonate. Hence, 0.06 M concentration of sodium
malonate was used for further studies while incomplete extraction of
iridium(III) was found to be in sodium salicylate and in sodium succinate
(Fig. 7.3).
7.4.4 Effect of diluents
The studies were then performed to find out the most suitable solvent for
the extraction of the ion-pair complex of iridium(III).It was found that a 0.2 M
solution of n-octylaniline in benzene, toluene, xylene, n-butyl alcohol, amyl
alcohol, amyl acetate provides quantitative extraction of iridium(III). The
extraction of iridium(III) was incomplete if n-octylaniline is dissolved in
chloroform (44.7 %) while no extraction was observed in methyl isobutyl
ketone, 1,2-dichloroethane (Table 7.5). On safety ground, toluene was
preferred to other solvents.
7.4.5 Effect of equilibration time
The extraction of iridium(III) was studied for various time intervals in
the range of 10 sec - 20 min with 0.2 M n-octylaniline (Table7.6). It was
observed that, under the optimized experimental conditions a minimum 1 min
time interval was required for attaining equilibrium in the sense to extract
iridium(III) quantitatively. But with prolonged shaking over 12 min there was
decrease in the percentage extraction of iridium(III) due to the dissociation of
ion-pair complex. Hence, in all further studies the both phases were
equilibrated for 3 min. (Fig 7.4)
7.4.6 Effect of stripping agent
Iridium(III) from organic phase was stripped with the two 10 mL
portions of various stripping agents at different concentrations of mineral acids,
buffer solutions and some bases. Iridium(III) was quantitatively stripped with
hydrochloric acid (1.0 M to 5.0 M) (Table 7.7 ). However, percentage recovery
Chapter 7 Liquid‐liquid extraction of iridium(III) from malonate media using liquid anion exchanger
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur
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of iridium(III) from organic phase was found to be incomplete with strippants
as water, nitric acid (1.0 M to 3.0 M), sulphuric acid (1.0 M to 3.0 M) and
hydrobromic acid (1.0 M to 3.0 M) and there was no extraction in ammonia
buffer (pH 10), ammonia, sodium chloride. In recommended procedure, two
10 mL portions of 2.0 M hydrochloric acid were used for the complete
stripping of metal from loaded organic phase.
7.4.7 Effect of aqueous to organic volume ratio
The extraction of iridium(III) was carried out in different aqueous
volumes in the range 150-10 mL from 0.06 M sodium malonate medium with
10 mL 0.2 M n-octylaniline in toluene (Table 7.8). The quantitative extraction
of iridium(III) was observed when phase ratio, A/O, varied from 10:10 to
50:10. Therefore in the recommended procedure the phase ratio 2.5:1 was
maintained through the all experimental study.
7.4.8 Metal loading capacity of extractant
The influence of the initial iridium(III) concentration 25-3000 µg on the
extraction by 0.2 M n-octylaniline in toluene was studied. It was observed that,
varying the initial iridium(III) concentration in the range of 25-1300 µg has no
significant influence on iridium(III) extraction with the 10 mL of 0.2 M
extractant (Table 7.9). The maximum loading capacity of 10 mL 0.2 M solution
of n-octylaniline in toluene was found to be 1300 µg iridium(III).
7.4.9 Nature of extracted species
Attempts were made to ascertain the nature of the extracted complex
species using log D - log C plots. The graphs of log D[Ir(III)] against
log C[n-octylaniline] at fixed sodium malonate concentration (0.06 M) were found to
be linear and having slopes of 1.2 and 1.3 values at pH 5.0 and 6.0, respectively
(Fig. 7.5). Also plots of log D[Ir(III)] against log C[malonate] at fixed
n-octylaniline concentration (0.2 M) were linear and slope values were found to
be 1.9 and 2.0 at pH 5.0 and 6.0, respectively (Fig. 7.6). The probable
composition of extracted species was calculated to be 1:2:1 (metal : acid :
Chapter 7 Liquid‐liquid extraction of iridium(III) from malonate media using liquid anion exchanger
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur
240
extractant). The possible mechanism of extracted species appears to be
protonated n-octylaniline which forms cationic species as
[CH3(CH2)7C6H4NH3] +(org) , while malonate (bidented ligand) combines with
iridium(III) to form anionic species as Ir(C3H2O4)-2(aq) and both of them unite
to form ion-pair of the type [CH3(CH2)7C6H4NH3+ Ir(C3H2O4)-
2]org which being
neutral constituted extractable species. CH3(CH2)7C6H4NH2(org)+ H+ CH3(CH2)7C6H4NH3
+(org) (7.1)
Ir3+(aq)
+ 2C3H2O4-(aq) Ir(C3H2O4)2
-(aq) (7.2)
CH3(CH2)7C6H4NH3+
(org)+ Ir(C3H2O4)2-(aq) [CH3(CH2)7C6H4NH3
+Ir(C3H2O4)2-](org)(7.3)
7.4.10 Effect of diverse ions
The effect of various cations and anions on recovery of iridium(III) was
investigated. The tolerance limit was set as the amount of foreign ion causing a
change ± 2 % error in the recovery of iridium(III). It was observed that the
method is free from interference from a large number of cations and anions.
Initially the foreign ion was added to the iridium(III) solution in large excess;
100 mg for anions and 15 mg for cations. When interference was found to be
intensive, the tests were repeated with successively smaller amount of foreign
ion. The only species showing interference of Rh(III) was eliminated by
masking with citrate. The anionic species showing interference in the
procedure were EDTA, thiocyanate, thiosulphate (Table 7.10).
7.5 Applications
7.5.1 Separation and determination of iridium(III) from binary mixture
The separation of Ir(III) from some commonly associated metal ions
like Pt(IV), Pd(II), Ru(III), Au(III), Os(VIII), Se(IV), Te(IV), Fe(III), Co(II),
Ni(II) and Cu(II) using n-octylaniline can be achieved by taking advantage of
the difference in the extraction conditions of metal such as pH of the aqueous
phase, reagent concentration and use of masking agent (Table 7.11).
Rh(III) interfere in the extraction of Ir(III). Rh(III) and Ir(III) were
separated from each other by masking Rh(III) with 10 mg citrate. Iridium(III)
Chapter 7 Liquid‐liquid extraction of iridium(III) from malonate media using liquid anion exchanger
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur
241
was separated from these associated metal ions, under the optimum extraction
conditions of Ir(III) where, all the added metal ions were remained
quantitatively in aqueous phase from which they are determined
spectrophotometrically by standard methods [56- 61].
7.5.2 Determination of iridium(III) in a synthetic mixture
Iridum(III) was determined from multicomponent mixture where
associated metal ions are present in it. A solution containing 50 µg of
iridium(III) was taken and known amounts of other metals were added. The
extraction of iridium(III) was carried out using the method developed. The
results obtained were in good agreement with the amounts taken (Table 7.12).
7.5.2 Separation of iridium(III) from ternary mixtures
The method was extended to the determination of iridium(III) in some
synthetic mixtures of associated metal ions. The iridium(III) was extracted
using the proposed method and the results are presented in Table 7.13. Rh(III)
interfere in the extraction of Ir(III). Rh(III) masked with 10 mg citrate at the
time of extraction.
7.6 Conclusion
Quantitative extraction of iridium(III) was achieved in 3 min with 0.2 M
n-octyaniline in xylene at pH 8.0.
Extraction reaction occurred through anion-exchange mechanism.
Developed method is efficient for quantitative separation of iridium(III)
in presence of various interfering cations and anions.
The proposed extractive separation method is simple, rapid, selective
reproducible and suitable for separation and determination of
iridium(III) from associated metal ions and synthetic mixtures.
Chapter 7 Liquid‐liquid extraction of iridium(III) from malonate media using liquid anion exchanger
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur
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Table 7.2 Extraction of iridium(III) as a function of pH
Ir(III) = 50 μg Aq: Org = 2.5: 1
Sodium malonate = 0.06 M n-Octylaniline = 0.2 M in toluene
Equilibrium time = 3 min Strippant = 2 M Hydrochloric acid
(2×10 mL)
pH Percentage extraction,
(% E) Distribution ratio,
(D)
1.0 - -
2.0 - -
3.0 - -
4.0 29.8 1.06
5.0 47.9 2.29
6.0 66.2 4.89
6.2 72.3 6.52
6.4 83.0 12.20
6.6 88.1 18.50
6.8 93.9 38.15
7.0 100 ∞
7.5 100 ∞
8.0* 100 ∞
8.5 100 ∞
8.8 91.5 26.91
9.0 85.9 15.23
10.0 60.0 3.75
* Recommended for general extraction procedure
Chapter 7 Liquid‐liquid extraction of iridium(III) from malonate media using liquid anion exchanger
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur
243
Table 7.3 Extraction behaviour of iridium(III) as a function of
n-octylaniline concentration
Ir(III) = 50 μg Aq: Org = 2.5: 1
Sodium malonate = 0.06 M pH = 8.0
Equilibrium time = 3 min Strippant = 2 M Hydrochloric acid
* Recommended for general extraction procedure
n-Octylaniline, (M)
Percentage extraction, (% E)
Distribution ratio, (D)
0.01 - -
0.02 - -
0.03 - -
0.04 45.9 2.12
0.05 58.9 3.58
0.06 68.9 5.53
0.07 73.8 7.04
0.08 79.9 9.93
0.09 85.9 15.23
0.10 89.9 22.25
0.11 93.9 38.48
0.12 100 ∞
0.14 100 ∞
0.16 100 ∞
0.18 100 ∞
0.20* 100 ∞
0.22 100 ∞
0.24 100 ∞
0.28 100 ∞
0.30 100 ∞
Chapter 7 Liquid‐liquid extraction of iridium(III) from malonate media using liquid anion exchanger
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur
244
Table 7.4 Extraction behavior of iridium(III)as a function of weak
organic acid concentration
Ir(III) = 50 μg Aq: Org = 2.5: 1
n-Octylaniline = 0.2 M in toluene pH = 8.0
Equilibrium time = 3 min Strippant = 2 M Hydrochloric acid (2×10 mL)
Acid concentration
(M)
Sodium malonate Sodium salicylate Sodium succinate
% Ea Db % E Db % E Db
0.005 30.3 1.08 14.9 0.43 18.9 0.58
0.010 37.9 1.52 20.9 0.66 22.0 0.70
0.020 77.6 8.66 47.9 2.29 25.8 0.86
0.030 84.5 13.62 58.9 3.58 30.3 1.08
0.040 87.5 17.5 61.8 4.04 37.0 1.46
0.050 100 ∞ 48.8 2.38 46.9 2.20
0.055 100 ∞ 35.2 1.35 55.3 3.09
0.060* 100 ∞ 27.9 0.96 68.3 5.38
0.065 100 ∞ 20.0 0.62 51.3 2.63
0.070 98.2 137.38 11.0 0.30 50.0 2.5
0.080 89.9 22.25 10.3 0.28 38.8 1.58
0.090 85.2 14.39 - - 19.8 0.61
0.10 62.0 4.07 - - 12.9 0.37 * Recommended for general extraction procedure a = Percentage extraction b= Distribution ratio
Chapter 7 Liquid‐liquid extraction of iridium(III) from malonate media using liquid anion exchanger
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur
245
Table 7.5 Extraction behaviour of iridium(III) as a function of
diluents
Ir(III) = 50 μg Aq: Org = 2.5: 1
n-Octylaniline = 0.2 M pH = 8.0
Equilibrium time = 3 min Strippant = 2 M Hydrochloric acid
Sodium malonate = 0.06 M (2 × 10 mL)
Solvent Dielectric
constant, (ε)
Percentage extraction,
(% E)
Distribution ratio, (D)
Benzene 2.27 100 ∞
Xylene 2.30 100 ∞
Toluene* 2.38 100 ∞
Chloroform 4.80 44.7 2.02
Methyl isobutyl ketone
13.10 No extraction -
n-Butyl alcohol 17.80 100 ∞
Amyl alcohol 13.90 100 ∞
Amyl aceate 13.90 100 ∞
1, 2-Dichloroethane 10.50 No extraction -
* Recommended for general extraction procedure
Chapter 7 Liquid‐liquid extraction of iridium(III) from malonate media using liquid anion exchanger
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur
246
Table 7.6 Extraction behavior of iridium(III) as a function of
equilibrium time
Ir(III) = 50 μg Aq: Org = 2.5: 1
n-Octylaniline = 0.2 M toluene pH = 8.0
Strippant = 2 M Hydrochloric acid Sodium malonate = 0.06 M
(2×10 mL)
Time in min Percentage extraction,
(% E )
Distribution ratio,
( D )
10 sec 32.3 1.19
15 sec 43.7 1.94
30 sec 74.5 7.30
1 100 ∞
2 100 ∞
3* 100 ∞
4 100 ∞
5 100 ∞
6 100 ∞
7 100 ∞
8 100 ∞
9 100 ∞
10 100 ∞
12 100 ∞
14 93.9 38.48
16 89.2 20.64
18 58.8 3.56
20 41.9 1.80
* Recommended for general extraction procedure
Chapter 7 Liquid‐liquid extraction of iridium(III) from malonate media using liquid anion exchanger
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur
247
Table 7.7 Extraction behavior of iridium(III) as a function of
stripping agents
Ir(III) = 50 μg Aq: Org = 2.5: 1
n-Octylaniline = 0.2 M toluene pH = 8.0
Sodium malonate = 0.06 M
Strippant M / pH Percentage extraction,
(%E )
Ammonia
1-10
No stripping
HCl*
1-5
100
H2SO4
1-3
47.3
HNO3
1-3
46.9
HBr
1-3
89.9
Water
-
10.2
NaCl
1-5 %
No stripping
Ammonia buffer pH-10 No stripping
* Recommended for general extraction procedure
Chapter 7 Liquid‐liquid extraction of iridium(III) from malonate media using liquid anion exchanger
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur
248
Table 7.8 Extraction of iridium(III) as a function of aqueous to organic
volume ratio
Ir(III) = 50 μg
n-Octylaniline = 0.2 M toluene pH = 8.0
Strippant = 2 M Hydrochloric acid Sodium malonate = 0.06 M
(2 × 10 mL)
* Recommended for general extraction procedure
Aqueous to organic volume ratio
Percentage extraction,
( % E )
Distribution ratio, ( D )
10:10 100 ∞
20:10 100 ∞
25:10* 100 ∞
30:10 100 ∞
35:10 100 ∞
40:10 100 ∞
50:10 100 ∞
70:10 93.7 37.18
100:10 61.3 3.95
150:10 36.1 1.41
Chapter 7 Liquid‐liquid extraction of iridium(III) from malonate media using liquid anion exchanger
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur
249
Table 7.9 Metal loading capacity of n-octylaniline
Ir(III) = 50 μg Aq: Org = 2.5: 1
n-Octylaniline = 0.2 M toluene pH = 8.0
Strippant = 2 M Hydrochloric acid Sodium malonate = 0.06 M
(2×10 mL)
Ir(III), ( μg ) Percentage extraction,
( % E )
Distribution ratio,
( D)
25 100 ∞
50* 100 ∞
100 100 ∞
200 100 ∞
300 100 ∞
400 100 ∞
600 100 ∞
800 100 ∞
1000 100 ∞
1200 100 ∞
1300 100 ∞
2000 87.9 18.16
2500 70.9 6.09
3000 44.8 2.02
* Recommended for general extraction procedure
Chapter 7 Liquid‐liquid extraction of iridium(III) from malonate media using liquid anion exchanger
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur
250
Table 7.10 Effect of foreign ions on the extraction of 50 μg iridium(III)
at pH 8.0 in 0.06 M sodium malonate with 0.2 M n-octyaniline
in toluene
a = Masked with 10 mg citrate.
Ratio of ions
Iridium: ion
Mass tolerated /
mg Foreign ion
2:150
15
Bi(III), Nitrate , fluoride
2:100
.
10
V(V), Mn(II), Mg(II), Ni(II), Co(II), Pb(II), Cu(II), Zn(II), Se (IV), Cd(II), Sn(II), Tl(III), citrate, ascorbate, thiourea, Cr(III), Ti(IV).
2:50
5
Ti(IV), Cr(VI), Fe(III), Sb(III), U(VI), W(VI), Mo(VI), Te(IV), Hg (II).
2:20
2
Au(III), Ag (I)
2:1
1
Ru(III), Os(VIII)
2:0.5
0.5
Rh(III) a Pt(IV), Pd(II)
Chapter 7 Liquid‐liquid extraction of iridium(III) from malonate media using liquid anion exchanger
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur
251
Table 7.11 Separation of iridium(III) from binary mixtures
*average of five determinations. a = masked by 10 mg by citrate.
Amount of metal ion,
(μg)
Mass taken/µg
Average (%) recovery*
Chromogenic ligand
Ref. No.
Ir(III) Rh(III)a
50 100
99.0 97.4
stannous chloride-hydrobromic acid
[56]
Ir(III) Ru(III)
50 200
99.9 98.9
4’-ChloroPTPT
[57]
Ir(III) Pt(IV)
50 300
99.0 99.4
stannous chloride-hydrochloric acid
[56]
Ir(III) Pd(II)
50 200
98.8 98.4
4’-ChloroPTPT
[57]
Ir(III) Au(III)
50 200
98.8 97.1
SnCl2
[56]
Ir(III) Se(IV)
50 200
99.0 97.0
4’-BromoPTPT
[59]
Ir(III) Te(IV)
50 200
98.8 98.9
4’-BromoPTPT
[60]
Ir(III) Os(VIII)
50 200
98.0 99.3
Thiourea
[56]
Ir(III) Fe(III)
50 500
99.0 98.8
Thiocynate
[56]
Ir(III) Cu(II)
50 1000
99.0 98.7
4’-ChloroPTPT
[61]
Ir(III) Ni(II)
50 1000
99.0 98.9
DMG
[58]
Chapter 7 Liquid‐liquid extraction of iridium(III) from malonate media using liquid anion exchanger
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur
252
Table 7.12 Analysis of synthetic mixture for iridium(III) content from
associated elements
Composition, µg Ir(III) found
µg Recovery* % RSD %
Ir(III), 50; Pd(II),100; Pt(IV),100.
49.8
99.6
0.4
Ir(III),50; Pt(IV),100; Os(VIII),100.
49.9
99.8
0.2
Ir(III),50; Pt(IV),100; Ru(III),100.
49.8
99.6
0.4
Ir(III),50; Pd(II),100; Pt(IV),100;Rh(III)a,100; Ru(III),100.
49.7
99.4
0.6
Ir(III),50, Cu(II),1000; Ag(I),100;Au(III),100.
49.7
99.4
0.6
Ir(III),50; Pd(II),100;
Pt(IV),100;Rh(III)a,100;
Ru(III),100;Os(VIII).
49.8
99.6
0.4
a masked with 10 mg citrate *average of five determinations.
Chapter 7 Liquid‐liquid extraction of iridium(III) from malonate media using liquid anion exchanger
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur
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Table 7.13 Separation of iridium(III) from ternary mixtures
Metal ion
Amount taken,
μg
Ir(III) found
µg
Average recovery of iridium(III),*
% Ir(III)
Rh(III)a Pt(IV)
50 200 100
49.7 99.4
Ir(III)
Rh(III)a Pd(II)
50 200 200
49.7 99.4
Ir(III)
Cu(II) Ni(II)
50 200 100
49.4 98.9
Ir(III)
Pd(II) Cu(II)
50 200 200
49.5 99.0
Ir(III)
Pt(II) Au(III)
50 100 100
49.5 99.0
* Average of five determinations a masked with 10 mg citrate
Chapter 7 Liquid‐liquid extraction of iridium(III) from malonate media using liquid anion exchanger
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur
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0
10
20
30
40
50
60
70
80
90
100
0 1 2 3 4 5 6 7 8 9 10
pH
Perc
enta
ge E
xtra
ctio
n (%
E)
Fig. 7.1 Plot of pH versus percentage extraction of iridium(III)
(50 μg/mL) from malonate medium (0.06 M) by using
n-octylaniline (0.2 M) as an extractant in toluene with 3 min
shaking time.
Chapter 7 Liquid‐liquid extraction of iridium(III) from malonate media using liquid anion exchanger
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur
255
0
10
20
30
40
50
60
70
80
90
100
0 0.05 0.1 0.15 0.2 0.25 0.3
n-octylaniline (M)
Perc
enta
ge E
xtra
ctio
n (%
E)
Fig. 7.2 Extraction of iridium(III) (50 µg/mL) at pH 8.0 from
0.06 M sodium malonate as a function of n-octylaniline
concentration.
Chapter 7 Liquid‐liquid extraction of iridium(III) from malonate media using liquid anion exchanger
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur
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0
10
20
30
40
50
60
70
80
90
100
0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.1
Weak Acid (M)
Perc
enta
ge E
xtra
ctio
n (%
E)
Sodium malonateSodium salicylateSodium succinate
Fig. 7.3 Extraction of iridium(III) (50 µg) with 0.2 M n-octylaniline at
pH 8.0 as a function of weak acid concentration.
Chapter 7 Liquid‐liquid extraction of iridium(III) from malonate media using liquid anion exchanger
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur
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0
10
20
30
40
50
60
70
80
90
100
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20Time in Min.
Perc
enta
ge E
xtra
ctio
n (%
E)
Fig. 7.4 Extraction of iridium(III) (50 µg/mL) at pH 8.0 from
0.06 M sodium malonate as a function of equilibration
period.
Chapter 7 Liquid‐liquid extraction of iridium(III) from malonate media using liquid anion exchanger
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur
258
■ Slope = 1.2 at pH 5
▲ Slope= 1.3 at pH 6.0
-0.1
0
0.1
0.2
0.3
0.4
-1.4 -1.3 -1.2 -1.1 -1 -0.9
Log C [n-octylaniline]
Log
D[I
r(II
I)]
Fig. 7.5 Log-log plot of distribution ratio D[Ir(III)] versus Log C[n-octylaniline]
at fixed malonate concentration.
Chapter 7 Liquid‐liquid extraction of iridium(III) from malonate media using liquid anion exchanger
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur
259
■ Slope = 1.9 at pH 5 ▲ S lope= 2.0 at pH 6
-0.9
-0.7
-0.5
-0.3
-0.1
0.1
0.3
0.5
0.7
0.9
-2.1 -1.9 -1.7 -1.5 -1.3 -1.1
Log C [malonate]
log
D[I
r(II
I)]
Fig. 7.6 Log-log plot of distribution ratio D[Ir(III)] versus Log C[malonate]
at fixed n-octylaniline concentration.
Chapter 7 Liquid‐liquid extraction of iridium(III) from malonate media using liquid anion exchanger
Analytical Chemistry Laboratory, Dept. of Chemistry, Shivaji University, Kolhapur
260
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